Cellulose polymers such as hydroxypropyl methylcellulose (“HPMC”) have long been recognized in the art as suitable aqueous film coatings for pharmaceutical tablets and the like. While it is common to use HPMC (and other similar polymers), it can be rather expensive. The available alternative for a non-enteric coating is a sugar coating. Though a sugar coating can be less expensive, can prevent moisture migration into the tablet substrate and can mask bad flavors, it is not as desirable as a film coating for all uses. For example, sugar coatings cannot be applied as thinly as a film coating, are not clear, and are not non-caloric. Furthermore, sugar coatings have a higher risk of cracking than do film coatings. Finally, sugar coatings are typically mixed with hot water prior to application, which is not always readily available.
Manufacturers faced with the need to provide a durable, virtually non-caloric, thin or clear coat on tablets or confectionaries must pay a relatively high amount per pound for HPMC, or live with the drawbacks of sugar coatings.
U.S. Pat. No. 5,591,455 to Signorino suggests using gum acacia, instead of or in addition to other ingredients, in combination with HPMC to make a “wet-powder” blend for aqueous film coating. Water and plasticizers are added to the wet-powder blend prior to application. However, there is no disclosure of the amount of gum acacia that is effective. This failure is critical since gum acacia has not previously been used as a film-former, and would not ordinarily be expected to be used as a film former. This is because gum acacia is traditionally used as a wetting agent, emulsifier or binder—applications that are markedly different from those in which film formers are generally used. Moreover, wet powder products, such as that disclosed in the Signorino patent, contains up to 30% water resulting in a heavier product that is significantly more costly to ship. In addition, the added moisture often negatively affects the shelf life of the blended ingredients (e.g., wet gum acacia can readily become moldy).
U.S. Pat. No. 5,470,581 to Grillo et al. discloses a dry-powder edible film-coating composition for use on pharmaceuticals and the like, comprising a dry mixture of a cellulosic polymer, maltodextrin and a plasticizer. The maltodextrin is used in quantities ranging from 5% to 78.5% by weight of the powder. Though maltodextrin is a film former that costs less than those generally used, i.e. hydroxypropyl methylcellulose, it does not perform as well because it yields a brittle coating that is prone to cracking.
Futhermore, U.S. Pat. No. 4,453,370 to Porter et al. discloses another dry-powder edible film-coating composition for use on pharmaceuticals and the like, comprising in part of powdered particles of a film forming non-toxic edible polymer and a pigment. However, the resulting film coating is not clear.
Therefore, there remains a need for a less-expensive, dry-powder film coating for pharmaceuticals and confectionaries that is clear and performs as well as a coating containing more expensive components.